Ferromagnetic Switching of Knotted Vector Fields in Chiral Liquid Crystal Colloids

Graduate Thesis Or Dissertation

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/tb09j596c

Abstract

We experimentally realize polydomain and monodomain chiral ferromagnetic liquid crystal colloids that exhibit solitonic and knotted vector field configurations. Formed by dispersions of ferromagnetic nanoplatelets in chiral nematic liquid crystals, these soft colloidal ferro-magnets exhibit spontaneous long-range alignment of magnetic dipole moments of individual platelets, giving rise to a continuum of magnetization field M(r). Competing effects of surface confinement and chirality prompt spontaneous formation and enable optical generation of localized twisted solitonic structures with double twist tubes and torus knots of M(r), which exhibit a strong sensitivity to direction and magnitude of weak magnetic fields of ~10 G. Numerical modeling, implemented through free energy minimization to arrive at field-dependent three-dimensional structures of M(r), shows a good agreement with experiments and provides insights into the corresponding physical underpinnings.

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